Canine Demodicosis

Demodicosis is a disease caused by Demodex canis, a mite thatnormally lives in the hair follicles of dogs. These mites passfrom the bitch to the nursing pups at about 3 days of age. Themite spends its entire life on the dog and it is not consideredcontagious to other dogs, cats, or humans. Because of geneticfactors and/or disorders of the immune system, the number ofmites on the skin may increase dramatically and lead to thedevelopment of lesions. The clinical signs associated withdemodicosis are highly variable and may include hair loss,redness of the skin, and recurring bacterial skin infections. There are two forms of demodicosis: juvenile onset and adultonset. They are additionally classified as either "localized" or"generalized." The disease is generalized if two or more feetare affected; if five or more small circular areas of hair loss,scale, and redness are seen; or if an entire body region isaffected. Dogs with generalized demodicosis should not be bredbecause the defect in the immune system that allows them todevelop the disease is believed to be inherited. Dogs with juvenile-onset demodicosis are younger than 18 monthsof age at the onset of clinical signs. The localized form of thedisease is considered benign and should not be treated becauseabout 80 per cent of these dogs naturally control their own mitepopulation within 2 to 3 months. Some develop generalizedjuvenile-onset demodicosis with hair loss, crusting, andirritation affecting the entire body. In addition to genetic andimmunologic factors, nutritional status, parasitic infections,heat cycles, and other diseases are considered potentiatingcauses. Adult-onset generalized demodicosis (dogs older than 18 monthsof age) is a serious disease because it may be an indication ofinternal disease that is altering or suppressing the immunesystem. Many of these dogs have received corticosteroids for aprolonged period of time. Clinical signs are similar to those inthe juvenile-onset generalized form of demodicosis. Diagnostictests may be performed to investigate an underlying cause, suchas hyperadrenocorticism (excess cortisone production oradministration), hypothyroidism, systemic disease or organdysfunction, and cancer. Chemotherapy or other immunosuppressivedrug therapy may also lead to the development of adult-onsetgeneralized demodicosis. Demodicosis is usually diagnosed by obtaining deep skinscrapings and visualizing the mites under a microscope. Thepresence of more than one adult mite or of immature formsindicates disease. In some breeds, such as the Chinese Shar Pei,and in dogs with chronic disease, especially of the feet, a skinbiopsy may be necessary to diagnose demodicosis. Generalizeddemodicosis is a serious disease and must be treatedaggressively with drugs to control the mites and the secondarybacterial skin infections. Treatment of generalized demodicosisconsists of identification and correction of possible underlyingdiseases that have allowed the mites to proliferate as well asspecific therapy for the mites and treatment of accompanyingsecondary bacterial infections. Most treatments for demodicosisrequire months of intensive therapy. It is not unusual for your veterinarian to prescribe an extendedcourse of oral antibiotics to treat the deep bacterial skininfections that frequently accompany demodicosis. Othertreatments are available for demodicosis, but amitraz (Mitaban)is the only treatment for demodicosis that is approved by theU.S. Food and Drug Administration. In any treatment plan fordemodicosis, corticosteroids (topical or systemic) arecontraindicated. Your veterinarian may recommend that Mitaban dips initially beperformed in the veterinary hospital by qualified personnel toensure that the treatment is performed correctly as well as toobserve for side effects. Medium-haired and long-haired dogsshould be clipped every 3 to 4 weeks to facilitate adequatepenetration of the Mitaban dip. Dogs should be bathed with abenzoyl peroxide shampoo before each dip. The dip is mixed withwater according to the instructions given by your veterinarianin a well-ventilated room or outdoors. Rubber gloves should beworn and, using a sponge, the mixture applied thoroughly tosaturate the skin. The dip should be applied with the dogstanding in a washtub as the dip runoff is reapplied with asponge for a full 15 minutes. It is important to treat thefacial area, ears, and feet as these regions are commonlyaffected by demodicosis. Dogs that have demodicosis affectingthe feet should stand in the dip preparation for a minimum of 15minutes. The dip should not be rinsed off. Allow the dog to airdry. Your dog should not be allowed to become wet (including thefeet) between Mitaban treatments, as this washes off themedication. This procedure should be repeated as directed byyour veterinarian. A new mixture must be prepared for eachtreatment because the drug is unstable when exposed to light andair; for the same reason, any remaining dip should be discarded.The side effects of Mitaban include lethargy, skin irritation,itchiness, loss of appetite, and occasional vomiting ordiarrhea. Side effects are more commonly seen in small dogs,especially the toy breeds. If side effects are observed, yourveterinarian should be notified. Other drugs can help in the treatment of demodicosis. Thesesystemic drugs are ivermectin and milbemycin. If your dog hasnot received heartworm preventive on a regular basis, yourveterinarian needs to perform a blood test for heartworm diseasebefore administration of either of these drugs. The side effectsof ivermectin and milbemycin include decreased appetite,lethargy, weakness, dilated pupils, tremors, vomiting, coma, anddeath. Usually the more serious side effects occur withivermectin, but they may also occur with milbemycin. The sideeffects are rare and usually resolve with discontinuation of thedrug. Collies, Shetland sheepdogs, Old English sheepdogs,Australian shepherds, border collies, or their crosses shouldnot be treated with ivermectin. Your dog needs to be evaluated by your veterinarian every 4 to 8weeks. Skin scrapings are obtained at each visit and treatmentusually continues until two or three consecutive skin scrapingshave been negative. Treatment is discontinued at this time, andyour dog is reevaluated every 3 months for 1 year. Your dog isnot considered "cured" until 1 year has passed withoutvisualization of mites on skin scrapings. A small percentage ofdogs have chronic demodicosis and may require lifelong therapy. The above is general veterinary information. Do not beginany course of treatment without consulting your regularveterinarian. All animals should be examined at least once every12 months.